GL: Fix issue with EXTBlendFuncExtendedES3DrawTest The call to glBindFragDataLocationIndexedEXT was not being properly forwarded through ANGLE because we assumed that if its location was set, then its index was set, which is not always the case. Fixed this, and also added a link status check after linking so the error will properly propagate in the future. Bug: chromium:1099763 Change-Id: I28981c04a3f2d6a59c239b35b3f7eb0c7f586804 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2289653 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com> Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>